Without limiting the scope of the present invention, its background will be described with reference to producing fluid from a subterranean formation, as an example.
After drilling each of the sections of a subterranean wellbore and retrieving the drill bit and drilling string to the surface, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within each section of the wellbore. This casing string is used to increase the integrity of the wellbore by preventing the wall of the hole from caving in. In addition, the casing string prevents movement of fluids from one formation to another formation. Conventionally, each section of the casing string may be cemented within the wellbore before the next section of the wellbore is drilled. Accordingly, each subsequent section of the wellbore must have a diameter that is less than the previous section.
For example, a first section of the wellbore may receive a conductor casing string having a 20-inch diameter. The next several sections of the wellbore may receive intermediate casing strings having 16-inch, 13⅜-inch and 9 ⅝-inch diameters, respectively. The final sections of the wellbore may receive production casing strings having 7-inch and 4½-inch diameters, respectively. Each of the casing strings may be hung from a casing head near the surface. Alternatively, some of the casing strings may be in the form of liner strings that extend from near the setting depth of previous section of casing. In this case, the liner string will be suspended from the previous section of casing on a liner hanger.
It has been found, however, that rig time can be reduced by utilizing the casing string as the drill string for rotating a drill bit. As this procedure, referred to as casing while drilling, does not require the use of a separate liner or casing string to be run downhole after the retrieval of the drill bit and drill string, the time needed to drill, case and cement a section of wellbore can be reduced. Typically, when the casing string operates as the drill string to rotate the drill bit, particularly robust casing must be utilized.
Whether conventionally drilled or after performing as casing while drilling operation, once the well construction process is finished, the various steps of the completion process may begin. For example, hydraulic openings or perforations are typically made through the production casing string, the cement, if any, and a short distance into the desired formation or formations so that production fluids may enter the interior of the wellbore. In addition, the completion process may involve formation stimulation to enhance production, gravel packing to prevent sand production and the like. The completion process also includes installing a production tubing string within the well that extends from the surface to the production interval or intervals. The tubing may include sand control screen sections that are positioned adjacent to the perforated intervals.
It would be desirable to further reduce rig time by minimizing the number of trips downhole required to drill and complete a well. Accordingly, it would be desirable to combine certain aspects of the drilling operation and the completion operation into the same trip downhole. Therefore, a need has arisen for an apparatus and a method for completing an interval of a wellbore while drilling.